The present invention relates to a combustion engine and, more particularly, to an airflow control system for an internal combustion engine having series turbochargers.
An internal combustion engine may include one or more turbochargers for compressing a fluid, which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor driven by the turbine. The compressor receives the fluid to be compressed and supplies the compressed fluid to the combustion chambers. The fluid compressed by the compressor may be in the form of combustion air or an air/fuel mixture.
An internal combustion engine having series turbochargers may include a wastegate valve for achieving target boost at different altitudes by bleeding exhaust gases. As disclosed in U.S. Pat. No. 5,974,801 (issued to Houtz on Nov. 2, 1999), the engine speed, boost pressure, rack position, and barometric pressure may be monitored. The wastegate valve may then be actuated based on one or more of the monitored parameters.
When boost pressure optimization is a primary objective, a wastegate valve must be made of materials capable of withstanding the high pressures and high temperatures associated with high boost. Such materials can greatly increase the cost of wastegate valve. Further, when boost pressure optimization is a primary objective, fuel consumption is typically a secondary concern.
The present invention is directed to overcoming one or more of the problems as set forth above.
According to one exemplary aspect of the invention, an airflow system for an internal combustion engine having an intake manifold and an exhaust manifold is provided. The airflow system may include a first turbocharger including a first turbine coupled with a first compressor. The first turbine may be configured to receive exhaust flow from the exhaust manifold, and the first compressor may be configured to supply compressed air to the intake manifold. A second turbocharger arranged in series with the first turbocharger may include a second turbine coupled with a second compressor. The system may include a wastegate valve fluidly coupled with the exhaust manifold and movable between a first position and a second position. The first position allows fluid flow exhausted by the engine to bypass at least one of the first turbine and the second turbine, and the second position restricts fluid flow exhausted by the engine from bypassing the first turbine and the second turbine. The system may include a controller configured to restrict supply of pressurized air to the wastegate valve such that the wastegate is in the second position at times when at least one of (i) a monitored load of the engine is less than or equal to a predetermined load for a monitored speed of the engine, (ii) a monitored speed of the engine is less than or equal to a predetermined speed for a monitored load of the engine, and (iii) a monitored temperature of compressed air leaving the first compressor is less than or equal to a predetermined temperature.
According to another exemplary aspect of the invention, an internal combustion engine includes an intake manifold, an exhaust manifold, and first and second turbochargers arranged in series. The first turbocharger may include a first turbine coupled with a first compressor, wherein the first turbine is configured to receive exhaust flow from the exhaust manifold, and the first compressor is configured to supply compressed air to the intake manifold. The second turbocharger may include a second turbine coupled with a second compressor. A wastegate valve may be fluidly coupled with the exhaust manifold and movable between a first position and a second position. The first position allows fluid flow exhausted by the engine to bypass at least one of the first turbine and the second turbine, and the second position restricts fluid flow exhausted by the engine from bypassing the first turbine and the second turbine. A control valve may be operable to control supply of pressurized air to the wastegate valve. A controller may be electrically coupled to the control valve and configured to operate the control valve to restrict the supply of pressurized air to the wastegate valve such that the wastegate is in the second position at times when at least one of (i) a monitored load of the engine is less than or equal to a predetermined load for a monitored speed of the engine, (ii) a monitored speed of the engine is less than or equal to a predetermined speed for a monitored load of the engine, and (iii) a monitored temperature of compressed air leaving the first compressor is less than or equal to a predetermined temperature.
According to yet another exemplary aspect of the invention, a method of controlling airflow to an internal combustion engine having an air intake manifold and an exhaust manifold is provided. The method may include imparting rotational movement to a first turbine and a first compressor of a first turbocharger with exhaust air flowing from the exhaust manifold of the engine, and imparting rotational movement to a second turbine and a second compressor of a second turbocharger with exhaust air flowing from an exhaust duct of the first turbocharger. Air drawn from atmosphere may be compressed with the second compressor, and air received from the second compressor may be compressed with the first compressor. The method may include supplying compressed air from the first compressor to the air intake manifold, fluidly coupling a wastegate valve with the exhaust manifold, and monitoring at least one of engine load, engine speed, and temperature of the compressed air leaving the first compressor. The wastegate valve may be movable between a first position and a second position. The first position allows fluid flow exhausted by the engine to bypass at least one of the first turbine and the second turbine, and the second position restricts fluid flow exhausted by the engine from bypassing the first turbine and the second turbine. The method may also include selectively controlling the supply of compressed air to the wastegate valve such that the wastegate is in the second position at times when at least one of (i) the monitored load of the engine is less than or equal to a predetermined load for the monitored speed of the engine, (ii) the monitored speed of the engine is less than or equal to a predetermined speed for the monitored load of the engine, and (iii) the monitored temperature of the compressed air leaving the first compressor is less than or equal to a predetermined temperature.
According to still another aspect of the invention, a method of controlling airflow to an internal combustion engine is provided. The method may include compressing a stream of air in a first turbocharger, compressing a stream of air in a second turbocharger, and sensing an engine parameter indicative of performance. The method may also include comparing the sensed engine parameter with a predetermined engine parameter and controlling a supply of compressed air to a compressed air cavity of a wastegate on at least one of the first turbocharger and the second turbocharger in response to the comparison.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.